diff --git a/comfy/model_base.py b/comfy/model_base.py
index 88155b9ae..f5224a840 100644
--- a/comfy/model_base.py
+++ b/comfy/model_base.py
@@ -1524,6 +1524,20 @@ class WAN21(BaseModel):
 
         return out
 
+    def resize_cond_for_context_window(self, cond_key, cond_value, window, x_in, device, retain_index_list=[]):
+        # In-context streams slicing (Bernini)
+        if cond_key == "context_latents" and isinstance(getattr(cond_value, "cond", None), list):
+            dim = window.dim
+            out = []
+            for lat in cond_value.cond:
+                if lat.ndim > dim and lat.shape[dim] > 1 and lat.shape[dim] == x_in.shape[dim]:
+                    idx = tuple([slice(None)] * dim + [window.index_list])
+                    out.append(lat[idx].to(device))
+                else:
+                    out.append(lat.to(device))
+            return cond_value._copy_with(out)
+        return super().resize_cond_for_context_window(cond_key, cond_value, window, x_in, device, retain_index_list=retain_index_list)
+
 
 class WAN21_CausalAR(WAN21):
     def __init__(self, model_config, model_type=ModelType.FLOW, device=None):